As I said in the other thread, it'd be cool for her to do. No one epitomizes what the X factor is about like Britney. Britney became one of the biggest stars in the world even though many of her peers could outsing her. She was able to parlay her limited vocals, dance skills, charisma, beauty and charm into a successful career. She had that je ne sais quoi, that intangible, unexplainable "X factor" that sustained her career for 14 years now. Who better than her can discuss the importance of showmanship, drive, and the need for putting on an entire show?
And let's not bring up the lip-syncing -- Paula, Christina, J.Lo, Cheryl Cole, Kelly Rowland, Nicole Scherzinger all have lip synced at some point in their career. Many of the performers who've come on X Factor (UK and US) have lip synced on the show and on others. If it's brought up (which it won't because it didn't happen with anyone else), Britney should address it point blank.